Sharpening the edge of wind turbines

Controlled rubber flaps could help make wind turbines less noisy and generate more energy.

So say researchers at Risø DTU National Laboratory for Sustainable Energy in Denmark, where successful wind-tunnel tests have proven the flaps’ ability to help control loads on large wind-turbine blades.

Research team leader Helge Aagaard Madsen said the system – called CRTEF (Controllable Rubber Trailing Edge Flap) – would use a control system that relies on information from embedded sensors to direct the movement of the flaps. These sensors would detect local wind conditions along the blade.

Madsen said many wind turbines currently have pitched blades that control load as they turn. These pitched blades reduce loads by 25 to 30 per cent compared with no pitch at all, but the addition of flaps could increase that figure to 40 per cent or more.

By decreasing loads, Madsen said this gives manufacturers the option of using less material in the construction of the entire turbine, including the tower and the shaft.

Another bonus, he said, is that the rubber flap gives the turbine blade a sharper edge that produces less noise and a greater energy output.
The researchers tested their flaps in an open-jet wind tunnel at skylight manufacturer Velux in Denmark. The test involved a 2m-long section of a blade with a 1m chord and 15cm rubber flap covering the entire span.

Madsen said his group is currently optimising the design and working towards a full-scale version. ’We hope to have it ready for a full-scale megawatt test in a few years,’ he said.

The blade profile, which measures approx. 2 x 1 metres, set up in a test stand in the open jet wind tunnel at the company Velux in Denmark. Two types of sensors for measuring wind loading are mounted on the leading edge of the blade profile.